1. Technical Field
The present disclosure relates to a radar system and a target detection method for detecting multiple targets.
2. Description of the Related Art
Development of living environments or social infrastructures that allow people to live safely and comfortably has been an issue of increasing interest. Along with this trend, there is a need for sensing humans in everyday life for such purposes as monitoring of the behaviors or situation of an elderly person or a patient in a hospital room, or security such as tracking a person conducting suspicious acts among many pedestrians.
For these purposes, it is required to sense multiple persons separately from each other in an adverse environment rather than a favorable environment like a space with good visibility. For example, there is a need for sensing humans under abnormal conditions, such as an environment filled with smoke due to a fire, a dark place with no street light, or a space partitioned by walls or curtains. In short, it is required to detect humans with correct separation and track their actions in however adverse an environment. For decision of whether a detected target is a human being or not in such a situation, imaging for obtaining information from which the shape and characteristic motions of the target can be estimated is also as important as sensing.
One sensing means that can be used in such an environment is a radio wave sensor (a radar). Because of its ability to measure a relative velocity and a relative distance simultaneously and instantaneously, the radar has already been commercialized as sensing systems for vehicles in particular.
With a typical radar, however, interference occurs between targets when there are multiple target objects and they are close to each other in distance and/or speed of travel. This kind of interference is called correlated interference. In the presence of correlated interference, separation of individual signals and correct determination of their directions of arrival are not possible. Techniques for separating signals from multiple targets in such a situation include a radar device using a super-resolution antenna disclosed by Japanese Unexamined Patent Application Publication No. 2003-194919.
The configuration of the super-resolution antenna disclosed by Japanese Unexamined Patent Application Publication No. 2003-194919 is shown in FIG. 18. In the super-resolution antenna shown in FIG. 18, received signals corresponding to n pulses received by element antennas 11, 12, . . . , 1M are separated into n frequency components by target signal separator circuits 21, 22, . . . , 2M for received signals from the same range cell in a pulse sequence of each PRI, and the separated signals further branch into n signals and are weighted with different weight functions W0, W1, . . . , Wn−1, which are set by a weight setting circuit 3. Output signals for which the same weight function is set are input from the target signal separator circuits 21, 22, . . . , 2M to the same angle measurement computation circuit 41, 42, . . . , 4n, each of which determines and outputs the directions of arrival of the signals. This enables accurate estimation of the directions of multiple targets having different Doppler frequencies in the same range cell.